Phase Change Water Recovery for Space Station - Parametric Testing and Analysis 860986
Vapor Compression Distillation (VCD) technology for phase change recovery of potable water from wastewater has evolved as a technically mature approach for use aboard the Space Station. A program to parametrically test an advanced preprototype Vapor Compression Distillation Subsystem (VCDS) was completed by Life Systems for the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) during 1985.
In parallel with parametric testing, a hardware improvement program was initiated to incorporate and verify certain key improvements into the advanced preprototype VCDS following initial parametric tests. Specific areas of improvements included long-life, self-lubricated bearings, a lightweight, highly-efficient compressor and a long-life magnetic drive. These improvements are now incorporated and verification testing started.
The advanced preprototype VCDS was designed to reclaim 95% of the available wastewater at a nominal water recovery rate of 1.36 kg/h (3.0 lb/hr) and 308 K (95 F) condenser temperature. While this performance was maintained for the initial testing, a 300% improvement in water production rate (4.1 kg/h (9.0 lb/hr)) with a corresponding lower specific energy was achieved following incorporation of the improvements.
The paper presents a summary of the results of the parametric test program conducted. Testing involved the characterization of key VCDS performance factors (water production rate, water quality and specific energy) as a function of recycle loop solids concentration, distillation unit temperature and fluids pump speed. The objective of this effort was to expand the VCDS data base to enable defining optimum performance characteristics for flight hardware development. Based upon the parametric testing results which were obtained, projections are made for a Phase Change Water Recovery Subsystem for the Space Station based upon the VCD concept. The projected unit processes 18.1 kg/day (40.0 lb/day) of wastewater, weighs, 36.1 kg(79 lb), has a volume of only 0.21 m3 (7.4 ft3) and requires only 84 W of electrical power for a specific energy of 76.8 W-h/kg (35 W-hr/lb).